The present invention relates to fluid additives useful for fluid loss control, diversion, and plugging operations for use in subterranean formations. More particularly, the present invention relates to methods of using relatively insoluble borate material particulates in fluid loss control, diversion, and plugging operations.
Degradable materials are commonly employed in subterranean operations. For instance, water-hydrolysable materials such a polylactic acid, may be used in subterranean operations as fluid loss control particles, diverting agents, filter cake components, drilling fluid additives, cement additives, and the like. In some cases, the water-hydrolysable material may be capable of releasing a desirable degradation product, e.g., an acid, during its hydrolysis. The acid released by certain water-hydrolysable materials may be used to facilitate a reduction in viscosity of a fluid or to degrade a filter cake, as well as for numerous other functions in subterranean operations.
Subterranean treatment fluids are commonly used in stimulation, sand control, and completion operations. As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid.
An example of a subterranean treatment that often uses an aqueous treatment fluid is hydraulic fracturing. In a hydraulic fracturing treatment, a viscous fracturing fluid is introduced into the formation at a high enough rate to exert a sufficient pressure on the formation to create and/or extend fractures therein. The viscous fracturing fluid suspends proppant particles that are to be placed in the fractures to prevent the fractures from fully closing (once the hydraulic pressure is released), thereby forming conductive channels within the formation through which hydrocarbons can flow toward the well bore for production. In certain circumstances, a portion of the fracturing fluid may be lost during the fracturing operation, e.g., through undesirable leak-off into natural fractures present in the formation. Typically, operators have attempted to solve this problem by including a fluid loss control additive in the fracturing fluid. Many conventional fluid loss control additives permanently reduce the permeability of a subterranean formation, negatively affect the rheology of the treatment fluid in which they are used, and/or reduce the rate at which the fluid is allowed to penetrate or leak off into desirable locations within the subterranean formation. Moreover, while it may be desirable to control or prevent fluid loss for a given period of time, in some instances it may become desirable to later allow a treatment fluid to penetrate or leak off into that portion of the subterranean formation. Thus, costly and time-consuming operations may be required to reverse the effects of conventional fluid loss control additives on the treatment fluid and/or to restore permeability to those portions of the subterranean formation affected by the fluid loss control additives.
In addition to helping control the loss of fluid into the formation, additives may also be added to treatment fluids in order to divert the treatment toward desired areas within the formation. For example, it may be desirable to add a diverting agent toward the end of an operation treating a section of a subterranean formation such that the agent will then slow or stop the flow of further treatment fluid into that area, thus diverting later-placed fluid to other areas.
Numerous additives are used in the art to help control fluid loss or to divert treatment fluids in subterranean operations. However, the use of these conventional additives may give rise to other problems. In some instances, the fluid loss control additives and diverting additives used are toxic and thus may harm the environment; this problem may be aggravated because many are poorly degradable or nondegradable within the environment. Due to environmental regulations, costly procedures often must be followed to dispose of the treatment fluids containing such compounds, ensuring that they do not contact the marine environment and groundwater. In addition, some known materials require hydrocarbon treatments to remove them from the formation after they are placed or require a high temperature for removal, or a large volume of under-saturated liquid (such as for the removal of salts) to be removed.
Thus, it is desirable to have a fluid loss control or diverting agent that poses little or no risk to the environment and that is able to degrade over time and restore lost permeability.